The present invention relates to a scanning optical device and an image forming apparatus, which are applicable to printers (printing machines), copying machines, and compound machines of these machines, which are equipped with a scanning exposing system to scan a photoreceptor drum with a laser beam based on image information so as to form an electrostatic latent image.
In recent years, widely practically used are digital color copying machines which form a color image based on color document image data obtained by reading a document. According to color copying machines of this type, a color document image is read by a scanner and the document image data obtained from the color document image are once stored in an image memory. Thereafter, the document image data read from the image memory are subjected to image processing, and then the document image data after the image processing are transmitted to a color printer.
For example, a color printer employing an electrophotographying system is structured by an image forming section which forms a yellow (Y) color, a magenta (M) color, a cyan (C) color, and a black (BK) color image, a fixing section and an intermediate transfer belt. In the image forming section, an electrostatic latent image is formed for each image color based on document image data by a scanning exposing section with a polygon mirror on a photoreceptor drum electrically charged uniformly by a charging device.
This electrostatic latent image is developed by a developing device for each image color. Such electrically charging, exposing, and developing are performed so as to form a color toner image on the photoreceptor drum, and the color toner image is transferred onto a predetermined transfer material by a transferring section. The toner image transferred onto the transfer material is fixed by a fixing section. As a result, an image is formed based on document image data on the predetermined transfer material, whereby the document image can be copied.
At the time of forming such a color image, it is required to take synchronism among plural image forming sections to form plural different color toner images in such a way that a formation timing of each color toner image is matched to each other. Among the plural different color toner images, if a deviation takes place in the formation timing, the deviation is recognized as a color deviation which causes remarkable deterioration in image quality of a color image formed on a transfer material.
Patent document 1 discloses an image forming apparatus equipped with a mechanism which corrects a scanning exposing section of this type. According to this image forming apparatus, the scanning optical device is constituted by a laser light source, optical elements such as a cylindrical lens, a correcting section, one set of laser beam detecting sections a wire position detecting section, and the like. At the time of correcting a color deviation, the correcting section shifts optical elements, such as a cylindrical lens so as to correct the position of a scanning line on a photoreceptor drum.
The laser beam detecting section detects the upper limit and lower limit of a scanning position of a laser beam which passes through the cylindrical lens and scans on a photoreceptor drum. An optical synchronous sensor is used in the laser beam detecting section, and is structured to detect the synchronism status of a laser beam. A wire position detecting section is arranged at the reverse surface side of a mounting base plate of the cylindrical lens, and is structured to detect a shift distance of the cylindrical lens from an amount of displacement of a wire. Thus, when the scanning optical device is constituted in such a way, since a wire position detecting section can be arranged at a corner part of the apparatus which is distant from the cylindrical lens, the apparatus can be made in a compact size.    Patent document 1: Japanese Unexamined Patent Publication No. 2003-114394 (Page 6, FIG. 5 in its official document)
Incidentally, in an image forming apparatus which has a polygon mirror rotating member and deflects a laser beam so as to scan, there are the following problems.
i. In the scanning optical device which is disclosed by Patent Document 1, a correcting section to correct the attitude of a cylindrical lens is equipped with a wire position detecting section to detect the position of the cylindrical lens. This wire position detecting section is arranged at a position distant from the cylindrical lens on the reverse surface side (to a corner part of the apparatus) of a mounting base plate of the cylindrical lens.
When the wire position detecting section detects the shift distance of the cylindrical lens by an amount of displacement of a wire, it is required to remove play in a worm gear, a flat gear, a power transmission gear and the like. Namely, in order to minimize variation in driving force of the worm gear, the flat gear, the power transmission gear and the like, a mechanism which pulls these gears by a coil spring through a wire member is adopted.
However, in order to make a motor torque small, it is necessary to make the spring constant of a coil spring small. For this reason, when a coil spring having a small spring constant is employed in a mechanism to pull by a coil spring, a large installing space is needed for it. Therefore, there is a problem that the large installing space is contrary to space saving.
ii. Moreover, in the scanning optical device of Patent Document 1, it is necessary to align a mark board (follower piece) of a wire member with the center of a detecting range of the upper limit and lower limit to restrict the shift of the wire member in the sensor section for detecting a wire position.
However, since the mounting position of the wire position detecting section has no room sufficient to conduct alignment for the shifting direction of the wire member, it is difficult to align the mark board (follower piece) of the wire member with the center of the detecting range with good reproducibility.
Then, the present invention has been devised to solve the abovementioned problems, and an object of the present invention is to provide a scanning optical device and image forming apparatus in which the arrangement of a correcting section to correct the position of optical elements, such as a cylindrical lens is improved so as to be able to adjust the mounting position of the correcting section with spatial allowance, and to contribute to make the entire body of the apparatus in a small size.
The abovementioned object can be attained by the following structure which reflects one aspect of the present invention.
A scanning optical device, comprises
a light source to emit a light beam;
a deflecting section to deflect the emitted light beam so as to scan;
an optical element to make the scanning light beam converge; and
a correcting mechanism to correct an attitude of the optical element so as to adjust the converged position of the scanning light beam,
wherein at least a part of the correcting mechanism is arranged between the deflecting section and the optical element.